It is known from the literature (J. pr. Chem 35, 456; J. Org. Chem. 26, (1961) 792) that sodium thiobarbiturate and in turn thiobarbituric acid can be prepared by reacting thiourea with a sodium salt of diethyl malonate in an ethanolic medium, but the yield of thiobarbituric acid is an unsatisfactory 84% of theory. It is also known that thiobarbituric acid can be prepared by starting from thiourea, diethyl malonate and an alkali metal alcoholate. Depending upon the alkali metal alcoholate which is used, this process produces different yields, that is, 60% when sodium ethylate is used and as little as 37% of theory when the less expensive sodium methylate is used (Sbornik Statei Obshchei Khim. 2, 1273-4 (1953)). In addition to the entirely unsatisfactorily yields, such a process also has the disadvantage that it results in ethanol/methanol mixtures which require an additional step in the product isolation procedure.